2,2-Dibromo-3-nitrilopropionamide (DBNPA) is a well-known compound useful in aqueous systems due to its biocidal activity. DBNPA has proven especially useful in controlling the fouling of cooling towers due to slime accumulation and in removing slime from wood pulp prior to processing operations in the paper industry. See, for example, U.S. Pat. Nos. 3,751,444; 4,163,796;, 4,241,080; and 4,328,171.
For many antimicrobial applications, it is desirable to employ DBNPA in a liquid concentrate composition for ease of shipment, storage, and especially for dispersibility in aqueous systems. Due to its cost, availability, and safety, water would be an ideal solvent for use in preparing such concentrates. Unfortunately, since DBNPA is only slightly soluble in water and usually degrades after prolonged contact with water, its use in such concentrates has not been found to be acceptable. See for example, "Rates and Products of Decomposition of 2,2-dibromo-3-nitrilopropionamide", Exner et al., J. Agr. Food Chem., Vol. 21, No. 5, pp. 838-842.
Because water has an adverse impact upon DBNPA, various types of stabilizers and non-aqueous solvents have been utilized in preparing liquid formulations of DBNPA. A recent commercial group of stabilizers for DBNPA are the polyalkylene glycols as disclosed in U.S. Pat. No. 5,070,105.
Unfortunately, commercial formulations comprising DBNPA, a polyalkylene glycol such as tetraethylene glycol, and water are fairly expensive due to the cost of the polyalkylene glycol. In addition, the DBNPA still degrades significantly over the course of time. Yet another disadvantage of this formulation includes the environmental concerns associated with employing polyalkylene glycols.
One such environmental concern is that increased chemical oxygen demand of the industrial waste water, e.g., cooling tower effluent, results when DBNPA is employed with organic solvents such as polyalkylene glycols. Chemical oxygen demand represents the amount of oxygen consumed in the oxidation of organic and oxidizable inorganic material contained in the waste water. See Richard J. Lewis, Hawley's Condensed Chemical Dictionary, Twelfth Edition, 1993, p. 253. A high chemical oxygen demand is undesirable for a body of water whether the body be a wastewater treatment pool or a natural body of water.
A high chemical oxygen demand for a body of water is undesirable because biodegradation of microorganisms may cause oxygen depletion in said body of water. If the body of water is a wastewater treatment pool then oxygen depletion could be detrimental to the efficient operation of the wastewater treatment plant. If the body of water is a natural body of water then oxygen depletion could be detrimental to aquatic life which require oxygen for survival.
Formulations comprised of DBNPA and organic solvents contribute more chemical oxygen demand than if DBNPA is employed alone or with non-organic solvents because organic solvents serve as a feeding ground for microorganisms by providing nutrients. Therefore, even though the DBNPA may destroy a majority of the microorganisms before it degrades, a few microorganisms still survive. Those few microoganisms multiply very rapidly in the presence of an organic solvent. Therefore, when DBNPA-treated waste water containing an organic solvent is released to the environment, or even if it is in a closed system, chemical oxygen demand will increase significantly over time due to the rapidly multiplying microorganisms consuming oxygen in the water.
It would be desirable to discover liquid formulations of DBNPA that utilize water as a suspending medium and in which the DBNPA is protected to prevent or reduce the decomposition or degradation thereof. This type of formulation would not only reduce the chemical oxygen demand as compared to the present commercial formulations which employ polyalkylene glycols, but such a formulation would also be less expensive. It would also be advantageous if a wide range of concentrations of DBNPA could be employed in the formulations. Furthermore, it would be desirable if the formulations were insensitive to changes in temperature and electrolyte concentration.